Abstract:

At least one sensing region is formed on the bending sensor by providing a
flexurally elastic base cover which is interrupted in at least one
partial region of the sensing region or is structured using elevations
and/or depressions. At least one planar optical fiber core is generated
on the base cover. The optical fiber core has a greater index of
refraction than the base cover. The optical fiber core is covered by a
shroud. The optical fiber core has a greater index of refraction than the
shroud.

Claims:

1-14. (canceled)

15. A method for manufacturing a bending sensor, the method
comprising:forming at least one planar lightguide core on a flexurally
elastic base jacket, the planar lightguide core having a higher
refractive index than the flexurally elastic base jacket;forming a
covering jacket on the at least one planar lightguide core, the at least
one planar lightguide core having a higher refractive index than the
covering jacket; andforming a sensing region by at least one of
interrupting the flexurally elastic base jacket in at least one portion
of the sensing region and patterning the flexurally elastic base jacket
by at least one of elevations and depressions in a plane where the
flexurally elastic base jacket meets the at least one planar lightguide
core.

16. The method according to claim 15, further comprising:forming the
flexurally elastic base jacket on an elastic carrier,wherein the elastic
carrier is patterned in the at least one portion of the sensing region by
at least one of elevations and depressions, andwherein the at least one
of the elevations and depressions in the flexurally elastic base jacket
or the interruption in the base jacket are formed by at least one of the
elevations and the depressions in the carrier.

17. The method according to claim 16, wherein at least one of the
flexurally elastic base jacket and the covering jacket absorbs incident
light.

18. A method for manufacturing a bending sensor, the method
comprising:forming at least one planar lightguide core having a light
injection region and an light extraction region on a flexurally elastic
base jacket, the at least one planar lightguide core having a higher
refractive index than the base jacket;forming at least one sensing region
in a light path between the light injection region and the light
extraction region of the at least one planar lightguide core by producing
a covering jacket that covers the at least one planar lightguide core and
which is interrupted in at least one portion of the sensing region;
andforming in the at least one portion of the covering jacket of the
sensing region a jacket replacement, the jacket replacement being one of
having a refractive index different than the refractive index of the base
jacket and absorbing incident light.

19. The method according to claim 18, further comprising:forming at least
one groove in the flexurally elastic base jacket; andforming the at least
one planar lightguide core in the at least one groove in the flexurally
elastic base jacket.

20. The method according to claim 18, further comprising, arranging at
least one mirror on the at least one planar lightguide core, the mirror
adapted to deflect light in the at least one planar lightguide core
parallel to a plane of the flexurally elastic base jacket.

21. The method according to claim 20, wherein a prism having a mirrored
end is arranged at a first end of the at least one at least one planar
lightguide core.

22. The method according to claim 20, wherein a semi-transparent mirror is
arranged in the at least one planar lightguide core, the semi-transparent
mirror adapted to separate a forward traveling light and a returning
light in the at least one planar lightguide core.

23. The method according to claim 20, wherein the light injection region
and the light extraction region of the at least one planar lightguide
core are formed as a common light injection region and light extraction
region of the at least one planar lightguide core.

24. The method according to claim 18, further comprising:forming at least
two planar lightguide cores on the flexurally elastic base jacket;
andforming an optical coupler at the light injection region, the optical
coupler adapted to divide the light to be injected at the light injection
region between the at least two lightguide cores.

25. The method according to claim 18, the method further
comprising:providing at least one light source at the light injection
region of the at least one planar lightguide core.

26. The method according to claim 18, in which the at least one lightguide
core is applied to the flexurally elastic base jacket as a liquid
polymer, in accordance with a desired profile.

27. The method according to claim 18, wherein the at least one lightguide
core is applied to the flexurally elastic base jacket as liquid polymer
by a jet printing method in accordance with a desired profile.

28. The method as claimed in one of claims 15, wherein the at least one
lightguide core is applied to the flexurally elastic base jacket as
liquid polymer and is cured by means of a direct writing method in
accordance with a desired profile of the lightguide core.

29. The method according to claim 18, the method further comprising:
providing at least one light sensor at the light extraction region of at
least one of the at least one planar lightguide core, the flexurally
elastic base jacket, and a covering jacket formed on the at least one
planar lightguide core.

30. The method as claimed in one of claims 18, wherein the at least one
lightguide core is applied to the flexurally elastic base jacket as
liquid polymer and is cured by means of a direct writing method in
accordance with a desired profile of the lightguide core.

31. The method according to claim 15, further comprising, arranging at
least one mirror on the at least one planar lightguide core, the mirror
adapted to deflect light in the at least one planar lightguide core
parallel to a plane of the flexurally elastic base jacket.

32. The method according to claim 31, wherein a prism having a mirrored
end is arranged at a first end of the at least one at least one planar
lightguide core.

31. The method according to claim 15, further comprising:forming at least
one groove in the flexurally elastic base jacket; andforming the at least
one planar lightguide core in the at least one groove in the flexurally
elastic base jacket.

32. The method according to claim 15, further comprising:forming at least
two planar lightguide cores on the flexurally elastic base jacket;
andforming an optical coupler at the light injection region, the optical
coupler adapted to divide the light to be injected at the light injection
region between the at least two lightguide cores.

33. The method according to claim 15, the method further
comprising:providing at least one light source at the light injection
region of the at least one planar lightguide core.

34. A bending sensor comprising:a flexurally elastic base jacket;at least
one planar lightguide core formed on the flexurally elastic base jacket;a
covering jacket covering the at least one lightguide core; anda sensing
region formed by at least one of interrupting the flexurally elastic base
in at least one portion of the sensing region and patterning the
flexurally elastic base jacket by at least one of elevations and
depressions in a plane where the flexurally elastic base meets the planar
lightguide core,wherein a refractive index of the elastic base and the
covering jacket is less than a refractive index of the at least one
planar lightguide core.

35. The bending sensor according to claim 34, wherein the flexurally
elastic base jacket further comprises a jacket replacement portion in at
least one portion of the sensing region, the jacket replacement portion
having a higher index of refraction than the base jacket.

Description:

[0001]The invention relates to a method for manufacturing a bending
sensor, in particular a strip-shaped bending sensor for an impact sensor
device of a pedestrian protection system of a vehicle.

[0002]Studies have shown that a high proportion of fatal accidents in road
traffic involve pedestrians. For this reason, legislation initiatives are
under way aimed at making the provision of devices for protecting
pedestrians in the case of a collision with a vehicle compulsory in
modern motor vehicles.

[0003]There is a particularly high risk of injury for a pedestrian when
there is a collision between a vehicle and the distance between a
typically easily deformable engine hood and a rigid engine block is very
small. The arrangement of increasingly large numbers of electronic
components in the region of the engine compartment and the fact that
vehicles are of very compact design results in the engine compartment
being tightly packed with very rigid elements. If a collision occurs with
a pedestrian, there is therefore a high risk of severe head injuries if
the pedestrian's head impacts against the engine hood and therefore comes
into contact with the components located underneath the engine hood.

[0004]On the other hand, the risk of injury can be reduced greatly given a
sufficiently large distance of, for example, over 10 cm between the
engine hood and the engine components arranged underneath it, since the
engine hood can absorb a sufficiently large amount of energy as a result
of the deformation and can therefore brake the pedestrian's movement
comparatively gently.

[0005]In order to increase safety of pedestrians in road traffic, the
European Automobile Manufacturers' Association (ACEA), for example, has
given a commitment to the authorities of the European Union to halve the
number of traffic deaths involving pedestrians by the year 2010 by means
of measures in vehicles. One measure for this purpose is to construct
vehicles with correspondingly spaced engine hoods. However, this is
frequently impossible due to the required compactness of vehicles.

[0006]In order to ensure sufficient attenuation in the event of a
collision with a pedestrian, it has been proposed, if an impact of a
person against the vehicle is detected, to raise the engine hood by more
than 10 cm from its closed position in order to provide a sufficient area
for deformation. The need for such safety systems to be not only reliable
but also very cost-effective presents an enormous challenge for these
systems.

[0007]For example, an article in the specialist journal "Automotive
Engineer", April 2004, page 48 ff., discloses, as an actuator for raising
the engine hood, a spring-based actuator whose spring is prestressed and
in the event of a detected collision is released, with the result that
the engine hood is correspondingly raised. However, pyrotechnic actuators
are also known from the abovementioned article.

[0008]CA 2 424 708 A1 discloses a method and a device for detecting a
collision between a vehicle and an object. Lightguide fibers are arranged
along a front bumper of the vehicle. The lightguide fibers comprise, in
their fiber jacket, light exiting regions which are arranged along the
lightguide fibers. A collision causes the lightguide fibers to bend. The
attenuation of the light which is transmitted in the lightguide fibers
changes as a result of the bending of the lightguide fiber if the
lightguide fiber is bent in the light exiting region. A signal is
acquired from the light which is modulated in this way and said signal is
processed in a signal processor. A safety device, for example for raising
an engine hood, can be activated in this way.

[0009]The object of the invention is to provide a method for manufacturing
a bending sensor which is simple and cost-effective.

[0010]The object is achieved by means of the features of the independent
patent claims. Advantageous developments of the invention are
characterized in the subclaims.

[0011]According to a first aspect, the invention is characterized by a
method for manufacturing a bending sensor. At least one sensing region is
formed on the bending sensor by providing a flexurally elastic base
jacket which is interrupted in at least one partial region of the sensing
region or is patterned by means of elevations and/or depressions. At
least one planar lightguide core is produced on the base jacket. The
lightguide core has a higher refractive index than the base jacket. The
lightguide core is covered by a covering jacket. The lightguide core has
a higher refractive index than the covering jacket.

[0012]The advantage is that, in the at least one partial region, total
reflection at a boundary between the lightguide core and the base jacket
is eliminated for some of the light which can be guided in the lightguide
core. As a result, a light exiting region is formed in the at least one
partial region. Depending on the bending of the bending sensor, the
degree of exiting of the light and therefore attenuation of the light in
the respective lightguide core is variable. A further advantage is that
the base jacket and/or the covering jacket do not have to be removed, and
the at least one light guide core does not have to be post-processed in
order to provide the light exiting region. The at least one planar
lightguide core is easy and cost-effective to manufacture in different
shapes, with the result that the bending sensor can be manufactured very
easily in a way which is suitable for a desired application, for example
as a sensor strip for an impact sensor device of a pedestrian protection
system of a vehicle. In this context, the bending sensor can, in
particular, be formed so as to correspond to the respective shape of a
bumper.

[0013]In one advantageous refinement, a flexurally elastic carrier is
provided which is patterned in the at least one partial region of the
sensing region of the bending sensor by means of elevations and/or
depressions. The base jacket is formed on the carrier. The elevations
and/or depressions in the base jacket or the interruption in the base
jacket are formed by means of the elevations and/or depressions in the
carrier. This has the advantage that the base jacket can be applied
continuously to the carrier in a very easy and cost-effective way. The
patterning or the interruptions in the base jacket result automatically
at the locations predefined by the patterning of the carrier. The
patterning or the interruptions in the base jacket can thus be
manufactured very easily.

[0014]In a further advantageous refinement, the base jacket and/or the
covering jacket are replaced in the at least one partial region by a
jacket replacement whose refractive index differs from the refractive
index of the base jacket or which absorbs incident light. In particular,
the refractive index of the jacket replacement is higher than the
refractive index of the base jacket. This has the advantage that the loss
of light in the at least one partial region is dependent on the
refractive index of the jacket replacement, and that the loss of light
can be predefined very easily by suitably selecting the refractive index
of the jacket replacement.

[0015]According to a second aspect, the invention is characterized by a
method for manufacturing a bending sensor. At least one planar lightguide
core is produced on a flexurally elastic base jacket. The lightguide core
has a higher refractive index than the base jacket. At least one sensing
region is formed on the bending sensor, in a light path between a light
injection region and a light extraction region of the lightguide core by
producing a covering jacket which covers the at least one lightguide core
and which is interrupted in at least one partial region of the sensing
region. The covering jacket is replaced in the at least one partial
region by a jacket replacement whose refractive index differs from the
refractive index of the base jacket or which absorbs incident light.

[0016]The advantage is that, in the at least one partial region, a total
reflection at a boundary between the lightguide core and the covering
jacket is eliminated for some of the light which can be guided in the
lightguide core. As a result, a light exiting region is formed in the at
least one partial region. Depending on the bending of the bending sensor,
a degree of exiting of the light and therefore attenuation of the light
in the respective lightguide core is variable. A further advantage is
that the base jacket and/or the covering jacket do not have to be
removed, and the at least one lightguide core does not have to be
post-processed in order to provide the light exiting region. The at least
one planar lightguide core is simple and cost-effective to manufacture in
different shapes, with the result that the bending sensor can be
manufactured very easily in a way which is suitable for a desired
application, for example as a sensor strip for an impact sensor device of
a pedestrian protection system of a vehicle. In this context, the bending
sensor can, in particular, be formed so as to correspond to the
respective shape of a bumper. In addition, the loss of light in the at
least one partial region is dependent on the refractive index of the
jacket replacement. The loss of light can therefore be predefined very
easily by suitably selecting the refractive index of the jacket
replacement. In particular, the refractive index of the jacket
replacement is higher than the refractive index of the base jacket.

[0017]In a further advantageous refinement, at least one groove, in which
in each case a light guide core is produced, is formed in the base
jacket. The advantage is that as a result the lightguide core can be
manufactured particularly easily and precisely.

[0018]In a further advantageous refinement, at least one mirror is
arranged on the lightguide core for deflecting the light which can be
guided in the lightguide core parallel to a plane of the base jacket in
the lightguide core. As a result, the light which can be guided in the
lightguide core can be deflected to a greater degree in the lightguide
core than would be possible as a result of a minimum permissible radius
of curvature of the lightguide core without loss of the total reflection
at a boundary between the lightguide core and the base jacket or the
covering jacket. The light can therefore be guided very tightly and with
little space requirement for the profile of the at least one lightguide
core, and very easily parallel to the plane of the base jacket compared
to an unbent state of the bending sensor. The bending sensor can, as a
result, be made very compact and economical in terms of space. In
particular, a reversing region for possibly necessary routing back of the
lightguide core can be made particularly compact.

[0019]In this context it is advantageous if in each case a prism whose end
faces are mirrored is arranged at one end of the at least one lightguide
core. This has the advantage that the light can be reflected back into
the lightguide core. As a result, the light can be guided in opposite
directions through the lightguide core. The lightguide core therefore
does not have to be routed back, and a particularly compact design of the
bending sensor is therefore possible.

[0020]In this context it is also advantageous if a semi-transparent mirror
is located in the at least one lightguide core, separating the forward
travelling light and the returning light in the respective lightguide
core. This has the advantage that the forward travelling light and the
returning light can be separated easily and reliably. The
semi-transparent mirror can also be integrated very easily into the
lightguide core. As a result, the bending sensor can be made particularly
compact.

[0021]Alternatively, the light injection region and the light extraction
region of the respective lightguide core are embodied as a common light
injection region and light extraction region of the respective lightguide
core, that is to say the light injection region and the light extraction
region of the respective lightguide core are arranged at a common end of
the lightguide core. This has the advantage that the forward travelling
light and the returning light do not have to be separated and the bending
sensor can be made particularly compact. The light source which is
assigned to the respective lightguide core, and the light sensor which is
assigned to the respective lightguide core, can therefore be made
particularly compact and arranged closely one next to the other at the
common light injection region and light extraction region. In particular,
the light source and the light sensor of the respective lightguide core
can also be embodied as a common component and arranged at the common
light injection region and light extraction region. The bending sensor
can therefore be made particularly simple and compact.

[0022]In a further advantageous refinement, at least two lightguide cores
are formed on the base jacket. An optical coupler, which divides the
light which can be injected at the light injection region between the at
least two lightguide cores, is formed at the light injection region of
the bending sensor on the base jacket. The advantage is that the optical
coupler can be integrated easily and cost-effectively with the at least
two lightguide cores and therefore no additional components are necessary
for the optical coupler. In addition, only one light source for feeding
the at least two lightguide cores is therefore necessary.

[0023]In a further advantageous refinement, at least one light source is
embedded at the light injection region of the at least one lightguide
core, and/or a light sensor is embedded at the light extraction region of
the at least one lightguide core into the base jacket and/or into the
lightguide core and/or into the covering jacket. The advantage is that as
a result particularly reliable injection of the light into the respective
lightguide core or particularly reliable sensing of the light in the
respective lightguide core is possible. In addition, the embedding of the
at least one light source and/or of the at least one light sensor is easy
and cost-effective. A further advantage is that there is no need for
complex and expensive processing of the at least one lightguide core at
the light injection region and/or the light extraction region for the
injection or extraction of the light. In addition, no additional
components are necessary for the injection or extraction of the light.

[0024]In a further advantageous refinement, the at least one lightguide
core is applied to the base jacket as liquid polymer metered by a
dispenser in accordance with a desired profile of the lightguide core,
and is subsequently cured. The application of the polymer is carried out,
for example, by a fine hollow needle of the dispenser. As a result,
precise metering and precise embodiment of the profile of the lightguide
core are possible. In addition, the application of the polymer is
therefore easy, quick and cost-effective.

[0025]In an alternative refinement, the at least one lightguide core is
applied to the base jacket as liquid polymer by means of a jet printing
method in accordance with a desired profile of the lightguide core, and
is subsequently cured. This has the advantage that precise metering and
precise refinement of the profile of the lightguide core are possible. In
addition, the application of the polymer is therefore easy,
cost-effective and particularly quick.

[0026]In a further alternative refinement, the at least one lightguide
core is applied to the base jacket as liquid polymer and is cured by
means of a direct writing method in accordance with a desired profile of
the lightguide core.

[0027]This has the advantage that precise formation of the lightguide core
is possible, and that the lightguide core is therefore produced easily,
quickly and cost-effectively.

[0028]Exemplary embodiments of the invention are explained below with
reference to the schematic drawings, in which:

[0036]FIG. 8shows a functional principle of the second embodiment of the
light exiting region,

[0037]FIG. 9shows the sensor strip with a first embodiment of a deflection
region,

[0038]FIG. 10 shows the sensor strip with a second embodiment of the
deflection region,

[0039]FIG. 11 shows the sensor strip with a third embodiment of the
deflection region, and

[0040]FIG. 12 shows a flowchart of a method for manufacturing the bending
sensor.

[0041]Elements with the same design or function are provided with the same
reference symbols in all the figures.

[0042]A vehicle 1 has an impact sensor device 2 (FIG. 1). The impact
sensor device 2 has a sensing region 4 which is arranged along a bumper 3
of the vehicle 1. By means of the sensing region 4, the impact sensor
device 2 can detect an impact of an impact object 5. The impact object 5
may be, for example, a pedestrian. In addition, the vehicle 1 has an
evaluation unit 6 in which measurement signals which are supplied by the
impact sensor device 2 are evaluated, and depending on the profile of the
respective measurement signal an impact of the impact object 5 is
detected and, if appropriate, measures for protecting the impact object 5
or the vehicle occupants are initiated. The measures can be, for example,
slight raising of an engine hood of the vehicle or else firing of one or
more airbags.

[0043]The impact sensor device 2 comprises the evaluation unit 6 and a
sensor strip 7 which comprises a bending sensor or which forms the
bending sensor (FIG. 2). The sensor strip 7 has an inlet region 8, a
deflection region 9 and the sensing region 4. The evaluation unit 6
comprises light sources 33 and light sensors 34 which are coupled to the
sensor strip 7. Alternatively, the light sources 33 and/or the light
sensors 34 can also be arranged in the bending sensor. As a result of
bending of the sensor strip 7 in the sensing region 4, the attenuation of
the light in the sensor strip 7 changes. The evaluation unit 6 is
designed to sense this change in the attenuation.

[0044]FIGS. 3A and 3B present a first embodiment of a planar lightguide
structure of the sensor strip 7. The sensor strip 7, which forms the
bending sensor, comprises a flexurally elastic base jacket 10 which forms
a carrier 11. A planar lightguide core 12 is formed as a layered optical
waveguide on the base jacket 10. The lightguide core 12 is covered by a
covering jacket 13. The sensor strip 7 is, for example, approximately 1.5
to 2.5 meters long and is preferably only a few millimeters wide, for
example approximately 6 millimeters. The sensor strip 7 or the bending
sensor can, however, also be made shorter or longer or narrower or wider.
The lightguide core 12 preferably has a width of less than 500
micrometers. A width of 100 micrometers or less is particularly
advantageous. However, the lightguide core 12 can also be made wider.

[0045]A refractive index of the base jacket 10 and of the covering jacket
13 is preferably selected in such a way that the light which can be
guided in the lightguide core 12 experiences total reflection at a
boundary between the lightguide 12 and the base jacket 10 or the covering
jacket 13. For this purpose, the base jacket 10 and the covering jacket
13 are embodied in such a way that a refractive index of the lightguide
core 12 is in each case larger than the refractive index of the base
jacket 10 and of the covering jacket 13. The refractive index of the
covering jacket 13 is preferably the same as the refractive index of the
base jacket 10.

[0046]In addition, the base jacket 10 and the covering jacket 13 are
preferably manufactured from the same material. For example, the
lightguide core 12, the base jacket 10 and the covering jacket 13 are
manufactured from the same material, for example from a polyimide, an
epoxy resin or polymethylmethacrylate, abbreviated as PMMA. However, the
lightguide core 12 on the one hand and the base jacket 10 and the
covering jacket 13 on the other are doped differently, for example with
fluorine, so that they have a different refractive index.

[0047]The lightguide core 12 is preferably a polymer lightguide core which
is produced by applying the polymer in liquid form to the base jacket 10
and by subsequent curing of the polymer in a desired profile and in a
desired shape. For this purpose, the liquid polymer is preferably made
light sensitive, with the result that the liquid polymer can be cured by
exposure to light, for example by exposure to ultraviolet light.

[0048]FIGS. 4A, 4B and 4C show a second embodiment of the planar
lightguide structure of the sensor strip 7. The carrier 11 is embodied as
a separately prefabricated flexurally elastic component. The carrier 11
is manufactured, for example, from polyethylene, but can also be
manufactured from another material. The carrier 11 does not have to have
any particular optical properties. However, the carrier 11 is, depending
on the configuration of the bending sensor, preferably manufactured from
a light-absorbing material. The base jacket is formed on the carrier 11.
The lightguide core 12 is formed on the base jacket 10. The lightguide
core 12 is covered by the covering jacket 13.

[0049]FIGS. 5A, 5B and 5C show a third embodiment of the planar lightguide
structure of the sensor strip 7. A groove 14, in which the lightguide
core 12 is formed, is formed in the base jacket 10. The lightguide core
12 is covered by the covering jacket 13.

[0050]Basically the same conditions which have already been explained
above apply to the optical properties for all embodiments, in particular
the refractive indices, the lightguide core 12, the base jacket 10, the
covering jacket 13 and the carrier 11. Two or more than two lightguide
cores 12 can also be formed on the base jacket 10, and said lightguide
cores 12 preferably extend parallel to one another in the longitudinal
direction of the sensor strip 7.

[0051]For the functions of a bending sensor, the sensor strip 7 comprises
at least one light exiting region 16 in the sensing region 4. The at
least one light exiting region 16 is embodied in such a way that,
depending on the bending of the bending sensor in the light exiting
region 16, a different proportion of the light guided in the lightguide
core 12 can exit from the lightguide core 12. As a result, the light
which is injected into the lightguide core 12 experiences a different
degree of attenuation depending on the bending of the bending sensor in
the light exiting region 16. The current degree of bending of the bending
sensor can therefore be inferred from the attenuation of the light. If
more than one lightguard core 12 is provided, each lightguide core 12
preferably has the at least one light exiting region 16 at a different
position within the sensing region 4. As a result, the position of the
bending of the bending sensor can be determined as a function of the
attenuation of the light in the respective lightguide core 12.

[0052]FIG. 6 shows a first embodiment of the light exiting region 16. The
carrier 11 has patterning 15 in the form of elevations and/or depressions
in the light exiting region 16. When the base jacket 10 is formed on the
carrier 11, the base jacket 10 is interrupted in the light exiting region
16 by this patterning 15 of the carrier 11, or patterned in accordance
with the patterning 15 of the carrier 11 in the form of elevations and/or
depressions. When the lightguide core 12 is produced on the base jacket
10, the lightguide core 12 can therefore also be patterned in the light
exiting region 16. As a result of the patterning 15, the total reflection
in the light exiting region 16 at the boundary between the lightguide
core 12 and the base jacket 10 is therefore cancelled out by the
patterning 15 for a portion of the light in the lightguide core 12, with
the result that light can exit from the lightguide core 12. The carrier
11 is preferably designed in such a way that it absorbs light, with the
result that the portion of the light which emerges from the lightguide
core 12 is absorbed in the carrier 11.

[0053]When the bending sensor is bent in the light exiting region 16 in
what is referred to as a positive direction in which the light exiting
region 16 is stretched, more light is extracted from the lightguide core
12 through scattering and/or absorption than in an unbent state of the
bending sensor. Less light output can therefore be measured at the end of
the lightguide core 12 and the attenuation of the light in the lightguide
core 12 is increased. When the bending sensor in the light exiting region
16 bends in an opposed negative direction in which the light exiting
region 16 is compressed, the light loss is reduced and a larger light
output can be measured at the end of the lightguide core 12 than in the
unbent state of the bending sensor, and the attenuation of the light in
the lightguide core 12 is reduced.

[0054]FIG. 7 shows an alternative or additional embodiment of the light
exiting region 16. The base jacket 10 is interrupted in the light exiting
region 16 and replaced by a jacket replacement 17. Correspondingly, it is
likewise alternatively or additionally possible for the covering jacket
13 to be interrupted in the light exiting region 16 or replaced by the
jacket replacement 17. The refractive index of the jacket replacement 17
differs from the refractive index of the base jacket 10. The refractive
index of the jacket replacement 17 is preferably higher than the
refractive index of the base jacket 10. In addition, the refractive index
of the jacket replacement 17 is preferably smaller than or equal to the
refractive index of the at least one lightguide core 12. The refractive
index of the jacket replacement 17 can, however, also be smaller than the
refractive index of the base jacket 10 or larger than the refractive
index of the at least one lightguide core 12.

[0055]FIG. 8 shows a functional principle of the second embodiment of the
light exiting region 16 according to FIG. 7. A first light beam 18
impinges at a first angle 19 of incidence at the boundary between the
lightguide core 12 and the base jacket 10. The first angle 19 of
incidence is larger than a limiting angle for the total reflection at the
boundary between the lightguide core 12 and the base jacket 10, that is
to say the first light beam 18 experiences total reflection at the
boundary between the lightguide core 12 and the base jacket 10 and
therefore remains in the lightguide core 12. A second light beam 20 with
a second angle 21 of incidence which corresponds to the angle 19 of
incidence impinges at a boundary between the lightguide core 12 and the
jacket replacement 17. The refractive index of the jacket replacement 17
is higher than the refractive index of the base jacket 10. As a result,
the second angle 21 of incidence is lower than a limiting angle for total
reflection at the boundary between the lightguide core 12 and the jacket
replacement 17, that is to say the second light beam 20 does not
experience total reflection at the boundary between the lightguide core
12 and the jacket replacement 17, and therefore exits at least partially
from the lightguide core 12. A third light beam 22 also impinges with a
third angle 23 of incidence at the boundary between the lightguide core
12 and the jacket replacement 17. However, the third angle 23 of
incidence is larger than the second angle 21 of incidence and larger than
the limiting angle for total reflection at the boundary between the
lightguide core 12 and the jacket replacement 17. As a result, the third
light beam 22 experiences total reflection at the boundary between the
lightguide core 12 and the jacket replacement 17, that is to say the
third light beam 22 remains in the lightguide core 12. By suitably
selecting the refractive index of the jacket replacement 17 it is
therefore possible to predefine very precisely how much light in the
light exiting region 16 can exit from the lightguide core 12 given a
predefined degree of bending of the bending sensor in the light exiting
region 16.

[0056]The refractive index of the lightguide core 12 is, for example,
1.49, the refractive index of the base jacket 10 and of the covering
jacket 13 1.35, and the refractive index of the jacket replacement 17
1.42. The limiting angle for total refraction at the boundary between the
lightguide core 12 and the base jacket is then obtained as the arc sine
of the quotient formed between 1.35 and 1.49, and is approximately
65°. The limiting angle for total reflection at the boundary
between the lightguide core 12 and the jacket replacement 17 is
correspondingly obtained as the arc sine of the quotient formed between
1.42 and 1.49, and is approximately 72°.

[0057]The refractive index of the jacket replacement 17 can, for example,
also be selected to be approximately the same as or larger than the
refractive index of the lightguide core 12. However, in order to avoid an
excessively large loss of light, the light exiting region 16 then has to
be selected to be correspondingly small in its extent.

[0058]FIG. 9 shows a sensor strip 7 with a first embodiment of the
deflection region 9. The bending sensor comprises four lightguide cores
12 and an optical coupler 24. The optical coupler 24 divides the light
injected into a light injection region 25 among the four lightguide cores
12. The optical coupler 24 is embodied, together with the four lightguide
cores 12, as a further planar lightguide core.

[0059]Starting from the light injection region 25 at one end of the
carrier 11, the lightguide cores 12 are formed in the longitudinal
direction of the carrier 11 and parallel to one another. In the
deflection region 9, the lightguide cores 12 are arcuate and are then
routed parallel to one another and along the carrier 11 back to the end
of the carrier 11 to form a respective light extraction region 26 of the
four lightguide cores 12. In this context it is necessary to ensure that
a deflection radius of the respective lightguide core 12 does not
undershoot a predefined minimum deflection radius. If the minimum
deflection radius is undershot, the limiting angle for total reflection
at the boundary between the respective lightguide core 12 and the
respective base jacket 10 or the respective covering jacket 13 for the
light which can be guided in the respective lightguide core 12 is
undershot, with the result that the light is no longer guided in the
respective lightguide core 12 and at least partially exits from it.

[0060]FIG. 10 shows a second embodiment of the deflection region 9 with
reference to an individual lightguide core 12. The lightguide core 12 is
formed at a right angle in the deflection region 9 in a plane parallel to
the base jacket 10 on the base jacket 10. At every right angle of the
lightguide core 12 a mirror, in particular a micromirror, is embedded in
the lightguide core 12. For the return of the light, a first mirror 27
and a second mirror 28, which each deflect the light at an angle of
approximately 90°, are provided in the deflection region 9. As a
result, for the deflection of the light in the deflection region 9 it is
not necessary to take into account the minimum deflection radius, with
the result that the at least one lightguide core 12 can be made compact
in the deflection region 9 and formed with a low spatial requirement.
However, by providing at least one mirror in the at least one lightguide
core 12, and given suitable orientation of the at least one mirror with
respect to the profile of the at least one lightguide core 12, the light
can also be deflected at other angles.

[0061]FIG. 11 shows a third embodiment of the deflection region 9 with
reference to an individual lightguide core 12. The lightguide core 12
has, in the deflection region 9, a prism 29 which has a first mirrored
region 30 at a first end face, and a second mirrored region 31 at a
second end face. The first mirrored region 30 and the second mirrored
region 31 essentially correspond in terms of their function to the first
mirror 27 and the second mirror 28. However, the light is deflected in
such a way that in the lightguide core 12 it is returned in the direction
of the light injection region 25. A semi-transparent mirror 32 is
arranged in the lightguide core 12 in order to separate the proportion of
light which is guided from the light injection region 25 to the
deflection region 9, and the portion of light which is guided from the
deflection region 9 back in the direction of the light injection region
25. The semi-transparent mirror 32 is preferably arranged in the feed-in
region 8 near to the light injection region 25.

[0062]The light which is returned from the deflection region 9 in the
lightguide core 12 is partially deflected by the semi-transparent mirror
32 to the light extraction region 26 which is arranged, for example, at
an angle of approximately 90° to the light injection region 25 on
the lightguide core 12. The third embodiment of the deflection region 9
also has the advantage that by providing the prism with its mirrored end
faces for deflecting the light in the deflection region 9 the minimum
deflection radius does not have to be taken into account and the
respective lightguide core 12 can therefore be made compact and with a
low spatial requirement in the deflection region 9. As an alternative to
providing the semi-transparent mirror 32, the light injection region 25
and the light extraction region 26 of the respective lightguide core 12
can each be embodied as a common light injection region 25 and light
extraction region 26, and the respective light source 33 and the
respective light sensor 34 can be arranged at the respective common light
injection region 25 and light extraction region 26. The respective light
source 33 and the respective light sensor 34 are preferably then
embodiment as a common component.

[0063]The light source 33 is preferably embodied in the lightguide core
12, at the light injection region 25. The light source 33 is, for
example, a light emitting diode. It is also possible to provide, in each
case, a light source 33 in the light injection region 25 of each
lightguide core 12. Correspondingly, in each case a light sensor 34 is
preferably embedded in the lightguide core 12 at the respective light
extraction regions 26. The light sources 33 and/or the light sensors 34
can, however, also be embedded in the base jacket 10 or the covering
jacket 13 provided that the light from the respective light source 33 is
injected in a suitable way into the lightguide core 12 or extracted in a
suitable way from the lightguide core 12 towards the respective light
sensor 34. In each case a further mirror for deflecting light into the
respective lightguide core 12 or out of it can also be provided in the
respective light injection region 25 and/or light extraction region 26.

[0064]In the carrier 11 and/or in the base jacket 10 and/or in the
covering jacket 13, at least one mechanical reinforcing element can
additionally be provided. The at least one mechanical reinforcing element
is arranged, for example, as a mechanical reinforcing fiber parallel to
the at least one lightguide core 12. The at least one reinforcing element
is embedded in the carrier 11, the base jacket 10 or the covering jacket
13 during the manufacture of said components, for example.

[0065]The mechanical reinforcing elements are preferably arranged in such
a way that the at least one lightguide core 12 is arranged between
mechanical reinforcing elements. The diameter of the mechanical
reinforcing elements is preferably greater than a diameter of the at
least one lightguide core 12. As a result, the at least one lightguide
core 12 is particularly satisfactorily protected against forces
transverse with respect to its longitudinal direction. In particular it
is therefore possible to prevent compressive forces from acting
transversely with respect to the longitudinal direction of the at least
one lightguide core 12 on the at least one lightguide core 12. This is
advantageous since such compressive forces may cause the attenuation of
the light in the at least one lightguide core 12 to change, but the
impact sensor device 2 is intended only to sense bending of the sensor
strip 7 in the sensing region 4. In addition, the at least one lightguide
core 12 and the at least one mechanical reinforcing element are
preferably arranged in a planar fashion, one next to the other.

[0066]The at least one mechanical reinforcing element is preferably
manufactured from glass fiber reinforced plastic. The at least one
mechanical reinforcing element can, however, also be manufactured, for
example, from polyalkyleneterephthalates, for example Mylar films. In
addition, for example Kevlar or glass yarns can also be used to transmit
tensile forces, and plastic rods can also be used to protect against
transverse compressive forces.

[0067]FIG. 12 shows a flowchart of a method for manufacturing the sensor
strip 7. The method starts in a step S1. In a step S2, if appropriate the
carrier 11 is prepared and/or the patterning 15 on the carrier 11 is
formed. In a step S3, the base jacket 10 is either embodied as a carrier
11, or the base jacket 10 is formed on the separate carrier 11 which is
provided, if appropriate. In the light exiting region 16 which is
provided, the base jacket 10 is interrupted or patterned correspondingly
by means of the patterning 15 of the carrier 11, or the base jacket 10 is
interrupted, that is to say not formed, in the light exiting region 16
which is provided.

[0068]Alternatively or additionally, in a step S4 the jacket replacement
17 for filling in the interrupted base jacket 10 can be formed. In a step
S5, the at least one lightguide core 12 is formed on the base jacket 10.
In addition, the optical coupler 24 can also be formed together with the
at least one lightguide core 12. In addition, if appropriate, the at
least one light source 33, the at least one light sensor 34, the first
and the second mirror 27, 28 or further mirrors, the semi-transparent
mirror 32 or the prism 29 can, if appropriate, also be arranged on the
sensor strip 7 and preferably embedded in the respective lightguide core
12.

[0069]In a step S6, at least one lightguide core 12 is covered by means of
the covering jacket 13. As an alternative or addition to the step S6, the
covering jacket 13 is formed in such a way that it has interruptions
which are preferably replaced by the jacket replacement 17. The method
ends in a step S8. If appropriate, further steps can also be provided,
for example for embedding the at least one reinforcing element or for
producing a protective sleeve around the bending sensor.

[0070]Different manufacturing methods are suitable for producing the at
least one lightguide core 12 on the base jacket 10. For example, the at
least one lightguide core 12 is applied as a liquid polymer by means of a
metering method by means of a dispensing device, referred to as a
dispenser, with the desired profile to the base jacket 10 and
subsequently cured, for example by irradiation with ultraviolet light. In
this way, very find lightguide cores 12 of less than 100 micrometers in
width and more than a meter in length can be manufactured easily and
cost-effectively. Alternatively, the liquid polymer can also be printed
or sprayed onto the base jacket 10 with the desired profile by means of a
jet printing method, which can also be referred to as a spraying method,
and subsequently cured. In both methods, during the production of the at
least one lightguide core 12 the sensor strip 7 is preferably moved on a
carriage in the longitudinal direction under an essentially stationary
dispenser or printing head. As a result, the at least one lightguide core
12 can be manufactured very precisely and homogenously over a length of
more than a meter. A further manufacturing method for producing the at
least one lightguide core 12 is a direct writing method. The liquid
polymer is applied over a surface onto the base jacket 10 and
subsequently cured along the desired profile of the at least one
lightguide core 12 by exposure to light. The exposure to light can be
carried out by means of a correspondingly designed mask or directly by
means of a laser. Regions of the applied liquid polymer which are not
exposed to light are subsequently removed, for example by means of a
solvent.

[0071]The advantage is that by means of the aforesaid manufacturing
methods it is possible to form a plurality of lightguide cores 12 very
closely one next to the other. For example, 16 or else 32 lightguide
cores 12 can be reliably formed on a sensor strip 7 which is 6
millimeters in width. The light exiting region 16 in the sensing region 4
can be positioned and dimensioned very precisely, with the result that
the properties of the bending sensor can be predefined reliably and
precisely. By forming the lightguide cores 12 on a polyimide basis, it is
in addition possible to predefine a temperature-resistance value of up to
380° C.; lightguide cores 12 on an epoxy resin basis, are
temperature resistant up to 200° C. This is advantageous in
particular for use in motor vehicles. A further advantage is that the
sensor strip 7 can be manufactured very easily in accordance with the
desired shape. For example, bumpers of some motor vehicle models have a
V-shaped profile. The sensor strip 7 and the lightguide cores 12 which
are formed on them can be formed very easily in this V shape with the
result that the sensor strip 7 does not have to be subsequently given the
desired shape. In addition, the at least one lightguide core 12 can be
manufactured quickly, precisely and cost-effectively.